Positional determination of a user in a mobile communications system with emission diversity

ABSTRACT

The invention relates to a method for increasing the precision during the determination of system parameters dependent on the propagation delay, e.g. for a positional determination, in a mobile communications system with emission diversity, according to which a subscriber data signal and a reference signal are assigned to a subscriber. The subscriber data signal is emitted by at least two antenna devices on the emission side, whereas the reference signal is emitted exclusively by one antenna device on the emission side. The reference signal is used to precisely determine signal propagation delays, upon which the system parameters depend.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to PCTApplication No. PCT/EP03/06539 filed on Jun. 20, 2003, GermanApplication No. 10227853.9 filed Jun. 21, 2002 and European ApplicationNo. 02013828.5 filed Jun. 21, 2002, the contents of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a method for data transmission in a wirelesscommunication system in which a subscriber data signal is emitted on thetransmit side by way of at least two antenna devices.

With regard to wireless communication systems, in order to improve thequality of a data transmission so-called “diversity methods”, referredto for example as “space diversity methods” or as “polarizationdiversity methods”, are used.

With regard to a space diversity method used on the transmit side, acarrier frequency subscriber data signal to be emitted is delivered as auser data signal to at least two antenna devices which exhibit adifference of several wavelengths between one another and which have thesame polarization.

With regard to a polarization diversity method used on the transmitside, the subscriber data signal to be emitted is similarly delivered toat least two antenna devices which however exhibit differentpolarizations. Typically, two antenna devices are located in a commonantenna housing.

Diversity methods can be used both on the transmit side and also on thereceive side and serve to enhance the transmission quality by enhancingan observed receive situation.

With regard to wireless communication systems, such as for example inthe case of the GSM mobile radio system or in the case of the GERANmobile radio system, a transmit-side subscriber data signal for exampleis divided into two partial signals which are then delivered by way oftwo “carrier units” to two spatially separated antenna devices havingthe same polarization for emission. Since as a result of their designthe carrier units exhibit tolerances in the respective signal paths ofthe partial signals, the two partial signals are subject to differentsignal propagation delays in respect of emission. In addition, specificpropagation paths having different signal propagation delays and signalattenuations are produced for each individual partial signal in theradio field as a result of multipath propagation.

On the receive side, a superimposition of the individual partial signalstakes place with respect to the subscriber signal, whereby a so-called“diversity gain” is achieved in systems engineering terms. On the otherhand, a radio cell enlargement or a range extension can be achievedbetween sender and receiver by way of the diversity gain.

With regard to the receiver on the other hand, the different propagationpaths should be taken into consideration in an appropriate manner, whichimplies an increased complexity on the part of the receiver.

With regard to mobile radio systems, such as for example in the case ofthe GSM mobile radio system, a positional determination (locationservice) is carried out for the subscriber during a data transmissionbetween a mobile subscriber and a base station, using the so-called“Timing Advance Mechanism, TA” for example. In this situation, signalpropagation delays for a reference signal are determined during the datatransmission between subscriber and base station and these are used toascertain the position of the subscriber.

Inaccuracies in the positional determination can be attributed directlyto inaccuracies occurring whilst determining the signal propagationdelay of the reference signal.

With regard to the GSM mobile radio system, by using the TA mechanism itis possible to realize positional determinations having an accuracy ofabout 200 meters, whereby in addition to the TA mechanism furtherstandardized methods such as Assisted GPS (A-GPS), Enhanced ObservedTime Difference (E-OTD) and Cell ID Timing Advance (CITA) are known forpositional determination.

A positional determination can be carried out with a required level ofaccuracy in respect of a diversity method executed on the transmit sideonly with a high resource requirement, or cannot be carried out at all,as a result of the multipath propagation and the different signalpropagation delays in the respective carrier units.

Corresponding problems occur for runtime dependent or runtime criticalsystem parameters or system properties in respect of the datatransmission, for example in the case of a “synchronized handover” or a“pseudo-synchronized handover”.

A so-called hybrid transmit diversity method for transmission ofadjacent, successive time slots is known from WO 02/11315 A2. In thissituation, information is transmitted from a base station to a mobileterminal X during a first time slot with the aid of a so-called “DelayDiversity” method, while information is transmitted to a further mobileterminal Y with the aid of a so-called “Space Time Diversity” method.

A base station having a plurality of transmit antennas is known from US2002/0022502 A1. In this situation, a unidirectional channel istransmitted either by a first antenna or by a second antenna. Theswitchover between the two antennas takes place with the aid of apredetermined random selection.

Different transmit diversity methods for a CDMA-TDD wirelesscommunication system are known from “Transmit Diversity Applied on theCDMA/TDD Cellular Systems”, Hiramatsu et al, VTC 2000-Spring. 2000 IEEE51st Vehicular Technology Conference Proceedings, Tokyo, Japan, May15-18, 2000, Vol. 2 OF3, pp. 1170-1174, XP000968054. In this situation,for example the physical synchronization channel PSCH is transmitted bya “Time Switched Transmit Diversity” method in which the PSCH is emittedin alternate succession by way of two antennas. The Primary CommonControl Channel P-CCPCH is transmitted by a “Block Space Time TransmitDiversity” method in which the P-CCPCH is fed simultaneously to twoantenna branches, whereby a separate coding occurs in each antennabranch and the signals differing in their coding are emittedsimultaneously by way of two antennas. The Dedicated Physical ChannelDPCH is transmitted by a “Selective Transmit Diversity and TransmitAdaptive Antennas” method in which the DPCH is emitted simultaneouslywith differing weighting by way of two antennas.

A positional determination method for a subscriber device in a wirelesscommunication system is known from DE 100 31 178 A1. With regard to thismethod, a distinction is made between time critical data on the one handand time non-critical data on the other hand, whereby the time criticaldata is transmitted during a time critical window and the timenon-critical data is sent during a time non-critical window. Measurementsignals required for positional determination are sent during the timenon-critical windows in order not to adversely affect the transmissionof time critical information. The time critical information is dividedinto time slots and transmitted in periodically recurring frames.Reference signal transmission is performed for example only in the caseof every n-th frame. Transmission resources are saved as a result.

While it is true that in the case of n=I where a reference signaltransmission to an observed subscriber occurs in each frame a positionaldetermination for example would be extremely precise, a reliablewireless delivery to the subscriber would however become uncertain as aresult of the constant loss of the diversity gain.

When a positional determination is carried out using a timing advancemechanism, then the reference signal is delivered for emission by way ofone single antenna device, as a result of which ambiguities in thesignal propagation delay measurement for the reference signal arereduced with regard to the receiver.

In wireless communication systems employing time division multipleaccess methods, the reference signal is transmitted in a time slot,whereby this time slot or the burst used for the transmission can bedefined specifically for each wireless communication terminal devicemanufacturer.

In order to be able transmit manufacturer specific reference signals fordifferent manufacturers at the corresponding time slot position, thereference signals are stored on the transmit side—for example in thebase station—in manufacturer specific form in a table and can be calleddown. By this means it is possible for terminal devices from differentmanufacturers to be operated in the wireless communication system of anetwork provider.

A positional determination is performed periodically or at timeintervals selected at random.

With regard to the GSM mobile radio system or the GERAN mobile radiosystem, the reference signal is preferably transmitted with the aid ofthe so-called SCCH channel which is repeated in every tenth frame. Anextended training sequence of an SCH time slot being used forsynchronization is used as the reference signal.

A time slot being used for synchronization is used by mobile terminaldevices of adjacent cells for so-called “monitoring”, whereby anadjacent cell terminal device decodes the user information of the SCHchannel in the IDLE frame. Through the operator code contained in theuser information the adjacent cell terminal device recognizes whether ornot it is permitted to access the associated cell of the SCH channel. Byperiodically deactivating the transmit diversity method in only everyn-th frame, this ensures that adjacent cell terminal devices are able toobserve the supply area of the cell assigned to the SCH channel in anappropriate manner.

A positional determination is then carried out for example in the caseof every hundredth frame with the aid of a so-called “LocationMeasurement Unit, LMU” which is now already normally available as amodule in every base station. As an additional function, the LMU has ana priori knowledge of the frames to be used for positionaldetermination, or of their frame numbers. A communication terminaldevice of a subscriber determines propagation delays for the referencesignal and reports these back to the base station, whereby tolerancesrelating to the positional determination are reduced by repeatedmeasurements.

In an advantageous embodiment the reference signal of a subscriber isemitted alternately by way of the at least two antenna devices and areceive-side assessment of the measured reference signal propagationdelays takes place for each antenna device used. In the best case, thesmallest reference signal propagation delay corresponds to the so-called“line of sight” propagation path. For positional determinations to beadditionally performed, the antenna device ascertained in this manner ispreferably used for emitting the reference signal.

If more than two antenna devices are used for emission purposes, theprobability of detecting the line-of-sight propagation path increases,which results in a possible increase in the accuracy of the positionaldetermination.

In order to check the accuracy of the positional determination, theantenna devices for reference signal emission are alternated from timeto time, with a subsequent propagation time assessment.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome more apparent and more readily appreciated from the followingdescription of the preferred embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 shows a wireless communication system for executing the methodaccording to one aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout.

FIG. 1 shows a wireless communication system for executing the methodaccording to one aspect of the invention.

A base station BTS comprises six carrier units CU1 to CU6 for thetransmission of subscriber signals, which receive subscriber signalsthat are to be transmitted by way of a network core.

A subscriber data signal TN1, which is assigned to a first subscriberTN, is delivered for emission to two antennas ANT1 and ANT2 which areused to implement a transmit diversity method. A reference signal REF,which is similarly assigned to the first subscriber TN, is however onlyemitted by way of a first antenna ANT1.

The subscriber data signal TN1 and the reference signal REF which areemitted by the first antenna ANT1 are delivered by way of a propagationpath AP1 to the subscriber TN, while the subscriber data signal TN1which is emitted by a second antenna ANT2 is delivered by way of apropagation path AP2 to the subscriber TN.

If in the case of a GSM mobile radio system the reference signal REF istransmitted with the aid of an SCH synchronization channel, then thereference signal REF is emitted alternately by the two antennas ANT1 andANT2 as follows:

in the case of all even TDMA frames by way of the first antenna ANT1 and

in the case of all odd TDMA frames by way of the second antenna ANT2.

A BSS-SMLC then orders signal propagation time measurements which arebased on the reference signals REF of the even or odd TDMA frames. Thetime multiplex signaled by the BSS-SMLC is thus known both with regardto the local measurement unit LMU and also with regard to the mobilesubscriber TN.

The BSS-SMLC then evaluates the signal propagation delays for therespective propagation paths AP1 and AP2 and selects that propagationpath for future positional determinations which with a small signalpropagation delay best corresponds to a direct propagation path(line-of-sight criterion).

The invention has been described in detail with particular reference topreferred embodiments thereof and examples, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention covered by the claims which may include thephrase “at least one of A, B and C” or a similar phrase as analternative expression that means one or more of A, B and C may be used,contrary to the holding in Superguide v. DIRECTV, 69 USPQ2d 1865 (Fed.Cir. 2004).

1-10. (canceled)
 11. A method for data transmission in a wirelesscommunication system, comprising: emitting a subscriber data signalassigned to a subscriber from at least two antenna devices using adiversity method; emitting a reference signal assigned to the subscriberfrom only one of the at least two antenna devices; and measuringpropagation delay of the reference signal to determine runtime criticalsystem parameters for a positional determination of the subscriber. 12.The method according to claim 11, wherein the reference signal isemitted periodically at predefined time intervals.
 13. The methodaccording to claim 11, wherein the reference signal is emittedaperiodically at time intervals selected at random.
 14. The methodaccording to claim 11, wherein the antenna device used to send thereference signal is switched between the at least two antenna devices.15. The method according to claim 14, wherein when the antenna deviceused to send the reference signal is switched, the propagation delay iscompared for the at least two antenna devices, and for futurepropagation delay measurements, the antenna device used to send thereference signal is selected to be the antenna device associated thesmaller propagation delay
 16. The method according to claim 14, whereinwhen the antenna device used to send the reference signal is switched, acomparison is made, and for future propagation delay measurements, theantenna device most closely within line-of-sight of the subscriber isselected.
 17. The method according to claim 11, wherein the positionaldetermination is performed with a timing advance mechanism.
 18. Themethod according to claim 11, wherein the subscriber data signal and thereference signal are transmitted using a time division multiple accessmethod.
 19. The method according to claim 18, wherein the referencesignal is a training sequence transmitted in a time slot used forsynchronization.
 20. The method according to claim 19, wherein thewireless communication system is a GSM mobile radio system, and anextended training sequence of a synchronization time slot is used as thereference signal.
 21. The method according to claim 11, wherein thereference signal is selected from a plurality of manufacturer-specificreference signals, and the manufacturer-specific reference signals arestored on a transmit side in a table.
 22. The method according to claim11, wherein the at least two antenna devices have polarizationsorthogonal to one another.
 23. The method according to claim 11, whereinthe at least two antenna devices have the same polarization, but are ata fixed distance from one another.
 24. The method according to claim 12,wherein the antenna device used to send the reference signal is switchedbetween the at least two antenna devices.
 25. The method according toclaim 15, wherein the positional determination is performed with atiming advance mechanism.
 26. The method according to claim 25, whereinthe subscriber data signal and the reference signal are transmittedusing a time division multiple access method.
 27. The method accordingto claim 26, wherein the reference signal is a training sequencetransmitted in a time slot used for synchronization.
 28. The methodaccording to claim 27, wherein the wireless communication system is aGSM mobile radio system, and an extended training sequence of asynchronization time slot is used as the reference signal.
 29. Themethod according to claim 28, wherein the reference signal is selectedfrom a plurality of manufacturer-specific reference signals, and themanufacturer-specific reference signals are stored on a transmit side ina table.
 30. The method according to claim 29, wherein the at least twoantenna devices have polarizations orthogonal to one another.